(From Amblyopia 413 dull, and the eye)

Visus debilis. This is a debility of sight, absolute or relative, without any apparent opacity of the cornea o-interior part of the eye. See Amaurosis.

Hippocrates means by this word, in his Aph. xxxi sect. 3. the dimness of sight to which old people arc-subject.

Paulus and Actuarius use it to express a gutta serena, and the latter considers it as arising from a defect of the nervous influence. De Meth. Med. lib. ii. cap. 7.

The amblyopia comprehends, 1st, Myopia, or shortsightedness: 2dly, Presbytia, or seeing only at a great distance: 3dly and 4thly, Amblyopia tenebrarum and luminis. It is the dysopia of Cullen; and the amblyopia of some writers is the amaurosis of Cullen. The remedy for this complaint is not easily assigned.- The eyes of the myopes and presbytae are said to be defective in their form, either too convex or too flat; so that the pencil of rays terminates before or beyond the retina, and distinct vision is of course impossible. The latter is more generally true than the former; for it must be obvious, that a deeper orbit, and consequently a more distant retina, or a stronger refracting power of the lens, may equally produce short-sightedness. In either case, there is no remedy but using-glasses, about one number less than that which renders the vision perfectly distinct, or using the eyes to examine distant objects. Age however alone brings relief, and this at no long period before blindness ensues; yet it is more common for short-sightedness to continue to extreme old age, than for the short-sighted to be blind.

The presbytae can scarcely, in any instance, procure strong or perfect sight. The weakness of vision may be relieved by cold bathing; cold applications to the eye; frequent ablutions with water, to which about l-4th or l-6th of good brandy has been added, by drawing sparks, or by Galvanism. The amblyopia tenebrarum arises from imperfect perception, and may be relieved, if relieved, by the same means. The opposite complaint, on the contrary, the seeing only by night, arises from too great sensibility, which renders common light excessive in its powers; and the disease is truly "tenebrae per tantum lumen obortae." Age may lessen it, but medicines will have little effect. - See Wallis's Sauvages' Nosology of the Eyes, p. 151, etc. Amblyopia, Hydrophthalmica, i. e. Caligo humorum. See Caligo. It sometimes means also Amaurosis.